Magnetic induction accelerator



Feb. 5, 1946. D. w. KERST 2,394,070

MAGNETIC INDUCTION ACCELERATOR Filed June 2. 1942 4 Sheets-Sheet 1Inventor Fig. l.

b y His Attorney.

. Donald W. KeTst,

D. w. KERST 2,394,070

MAGNETIC INDUCTION ACGELERAIOR Feb. 5, 1946.

Filed June 2, 1942 A Sheets-Sheet 2 Mfg Invelhcor Donald .W. KeTso Hisfitorn ey.

Feb. 5, 1946. w, KERST 2,394,070

' MAGNETIC INDUCTION ACCELERATOR I Filed June 2, 1942 4 Sheets-Sheet sFig 3.

PHASE SHIFTER J2 Ihventor:

Donald W. Kerst,

H is Attorney.

Feb. 5, 1946.

D. w. KERST 2,394,070

MAGNETIC INDUCTION ACCELERATOR Filed June 2. 1942 Fig.6.

4 Sheets-Sheet 4 Inventor: Donald W. Kerst,

H is Attorney.

Patented Feb. 5, 1946 MAGNETIC INDUCTION ACCELERATOR Donald W. Kerst,Champaign, Ill., asslgnor to General Electric Company, 7 a corporationof New York Application June 2, 1942, Serial No. 445,465

10 Claims.

The present invention relates to apparatus for accelerating chargedparticles, such as electrons, by means of magnetic induction effects,and is especially applicable in connection with apparatus of the generalcharacter described in my prior U. S. Patent No. 2,297,305, patentedSeptember 29, 1942, said Patent being assigned to the General ElectricCompany, a corporation of New York.

Apparatus of the character referred to typically includes a closedvessel and a magnetic system for producing a time-varying magnetic fieldof such space distribution as to confine charged particles projectedwithin the vessel to a circular orbit along which the particles arecontinuously accelerated by the electric field produced as the magneticflux through the orbit increases in magnitude. When the particles havebeen accelerated to a high velocity, they may be diverted from theaccelerating orbit and used for the generation of X-rays or for theproduction of other useful effects.

A major problem in the operation of magnetic induction apparatus oithetype specified consists in the provision of suitable means for divertingthe orbitally moving particles after their acceleration has proceeded tothe desired degree. In one instance, the effective utilization of theaccelerated particles involves deflecting them sufficiently so that theymay be intercepted by an X-ray producin target positioned in proximityto the accelerating path, and it is one object of the present inventionto provide improved means by which this type of diversion may beaccomplished. A further object consists in the provision of anarrangement by which the acceler-- ated particles may be collected intoa more or less collimated beam for utilization outside the acceleratingvessel.

In general, the first of the above mentioned objects is accomplished inaccordance with the invention by the use of auxiliary field-producingmeans operative near the end of the accelerating period for producing asymmetrical disturbance of the magnetic field of such character as topermit expansion or contraction of the path of gyration of theaccelerated particles. The second object is accomplished by combiningwith an orbit-disturbing arrangement of the type just specified meansfor producing a highly localized deflecting force which is operativeafter the accelerated particles have experienced a predeterminedcritical deviation from their normal orbital path abruptly to remove theaffected particles from the influence of the accelerating field, i. e.by causing the particles to be projected bodying certain importantaspects of the inven-' tion; Fig. 2 is a'section taken on line 2-2 ofFig. 1; Fig. 2a represents on an enlarged scale certain electrodestructures shown in Fig. 2; Fig. 2b is a still further enlarged view ofpart of the structure of Fig. 2a, as seen in a different plane. Fig. 3is a schematic representation illustrating diagrammatically the coilsystem employed in producing the normal accelerating field of the deviceof Fig. 1; Fig. 4 is a further schematic view showing a coil systemusable to produce a diversion of accelerated particles from their normalorbit; Fig. 5 is a circuit diagram illustrating one mode of energizationof the coil systems of Figs. 3 and 4; Figs. 6 and 7 are relatedsectional views illustrating a further important aspect of theinvention; and Fig. 8 is an enlargement of a portion of the structure ofFig. 6.

Referring particularly to Fig. 1, there is shown in section a closedglass vessel l0 providing within it an annular chamber l I. As will beexplained in greater detail at a later point, the vessel in encloses acircular orbit in which electrons may b accelerated to a high voltage,say on the order of several million volts. The vessel is preferablyhighly evacuated, e. g. by connection to a vacuum pump (not shown) and ahigh resistance coating, such as an extremely thin layer of silver, isapplied to the interior surface of the vessel to prevent wall chargingand the like.

The accelerating mechanism comprises a magnetic structur havingrotationally symmetrical (i. e. circular) pole pieces l4, [5 which arecoaxial with the annular vessel Ill. These pole pieces are constitutedof laminated iron held in assembly by insulating rings l6 and havecentral portions ll and I8 which are of essentially planar character.Near their outer edges, the poles are of tapered configuration, asindicated at 20 and 2B. A. second or reverse taper is provided adjacentthe periphery of each pole piece (i. e. at 22 and 23) for the purpose ofproviding a desired shaping of the marginal field. For decreasing thereluctance of the path between the opposed pole faces ll and I8, thereis provided an insert in the form of two laminated iron cylinders 25,the component elements of the cylinders being held in assembly by meansof an. insulating casing 26 which surrounds them and being spaced fromone another and from the other elements of the magnetic structure byspacers 28. A bolt 28' holds these parts in clamped relation. Anexternally closed magnetic circuit between the base portions of the polepieces is provided by U-shaped iron cores 29 and 30 joined in end-toendrelation to form a unitary structure. The upper pole piece It issupported from this structure by a bolting connection secured to aninsulating plug 3! keyed into the interior of the pole piece.

The magnetic structure is excited by means of a pair of series connectedcoils 32 and 33 which surround the pole pieces 14 and I5 and which areenergized in such manner as to produce a time-varying flux in themagnetic circuit. The energizingmeans may appropriately be of thecharacter shown in Fig. 3 which illustrates diagrammatically a portionof the structure of Fig. 1.

The coils 32 and 33 are shown connected in series with one another andwith a condenser 35 which is assumed to be of such capacity as toresonate with the inductance of the coils at a frequency correspondingto the desired frequency of operation of the apparatus. (This may be,for

example, on the order of six hundred cycles per second althoughfrequencies differing widely from this value are also usable.) To supplythe losses of the resonant circuit thus formed the coils 32 and 33 maybe coupled to primary coils 31 and 38 which are directly energized froman A.-C. power source 39. A relatively small amount of power supplied bythe source 39 will serve to maintain the resonant system in excitedcondition.

Within the closed vessel I0 (Fig. 1) and also within the region ofinfluence of the magnetic field produced by the pole pieces I4 and 85there is provided a thermionic cathode 40 which, in connection withassociated electrodes 4! and 42 (Figs. 2a and 2b) serves to generate anintermittent stream of electrons. The electrodes ll) to 62 are supportedby a stem 43 and are supplied with potential and with heating current(i. e. in the case of the cathode 40) by lead-in wires 64 sealed intothe stem.

These electrons are afiected by the magnetic field in two ways. In thefirst place, since the field is in a direction transverse to the planeof the electron motion, it tends to capture the electrons and to causethem to follow a generally circular orbit. (This orbit should'beinwardly displaced from the region occupied by the injecting electrodes40 to 42 so that electrons drawn into the orbit are free to gyratewithout interception by the electrode structure.) Secondly, thetime-varying flux enclosed by the orbit of any particular electronnecessarily produces an electric field tending to accelerate theelectron. In this latter respect, the apparatus as a whole consistsessentially of a transformer with a secondary comprising a circular pathalong which the various electrons are accelerated. Although, in general,the voltage per turn in such a transformer is low, the electrons canachieve very high velocities (e. g. several million volts) because ofthe tremendous number of turns which they execute during a single cycleof the magnetic flux variation.

It has been shown that by a proper design of the magnetic structure thefield existing at the electron orbit may be caused to produce acentripetal force in balance with the centrifugal tendencies of theaccelerated electrons. In general, this result requires that thefollowing relationship be satisfied:

where is the flux included within the electron orbit, r is the radius ofthe electron orbit, and Hr is the field strength at the orbit. Thisequation obviously means that the flux must be twice as strong as thatwhich would be produced by a homogeneous field equal to the field Hrextending over the entire area enclosed by the orbital electron path.

The condition just specified may be realized by making the reluctance ofthe magnetic path greater by an appropriate amount at the electron orbitthan its average reluctance within the orbit. In order to maintain fixed'proportinality between the enclosed fiux and the guide field (i. e. thefield Hr) at all times during the accelerating pe riod, one may includein the magnetic path an air gap or its equivalent. It is readilypracticable to control the dimensions of such a gap from point to pointover the pole area in such a fashion as to effect the balanced relationof guide field and enclosed flux which is desired for the purposespecified above and which is further necessary for radial and axialstability of the electron orbit. This may be done, for example, by aconstruction such as that shown in Fig. l in which the pole faces areoutwardly tapered. (The reverse taper indicated at 22 and 23 is for thepurpose of controlling the edge fiux and does not produce any actualincrease in flux near the outer edge of the pole faces.)

As has been previously stated, the functioning of the electrodes 40, 4!and 42 is such as to inject electrons into the accelerating chamber atinterv mittent intervals, injection being preferably accomplished attimes when the magnetic field between the pole pieces l4 and i5 is nearits zero value. The electron bursts thus provided within the chamber areaccelerated by the electric field produced by the increasing magneticflux in accordance with the principles previously described. Assumingthe magnetic field to be of appropriate intensity, a total energy on theorder of several million electron volts may be acquired by theaccelerated electrons in a small fraction of a second. calculated thateach orbital gyration of a given electron produces an increase in itsenergy of 70 electron volts, and that as many as 400,000 gyrations maybe completed within the period of a single accelerating cycle.)

It is, of course, desirable to provide some practical way in which theenergy of the fully accelerated electrons may be effectively utilized.In the arrangement of Fig. 1 this is accomplished by so arrangingmatters that while the normal accelerating orbit of the electrons isinside the space occupied by the injecting electrode assembly, theelectron orbit may be expanded to cause the electrons to impinge on theexposed parts of the assembly as the end of the accelerating cycle isapproached." The resultant impact of the accelerated electrons (e. g. onthe exposed surface of the electrode 4|) which thus functions as atarget will produce X-rays of an intensity corresponding to the velocityof the electrons involved. These X-rays may, of course, be utilizedoutside the apparatus in any appropriate way, as for the (In aparticular construction. it has been examination of thick metallicobjects or other bodies.

In accordance with the present invention, expansion of the electronorbit is produced in a very eifective fashion by the use of auxiliaryfield-pro ducing means operable to cause a symmetrical disturbance ofthe field between the pole pieces it and i5. In the first instance, thismeans comprises a pair of similar coils i and 52 (Figs. 1 and 2) whichare respectively supported above and below the plane of the acceleratingorbit (i. e. by attachment to the tapered pole faces and 2!). Thesecoils are preferably connected in series and are arranged inside thecircumference of the normal electron orbit. (This last condition is tosome degree afiected by the shaping of the pole faces, and in certaininstances the coils may be of approximately the ame diameter as theaccelerating orbit.) With this arrangement the field of the coils whichis effective in the air gap between the pole pieces of the magneticstructure is such as to destroy the balance between the accelerating andguide fields. In particular, the flux within the electron orbit and theradial gradient of the magnetic field (i. e. the change in held withradial position) are both altered, the direction of change dependingupon the direction of the current in the coils 5i and 52. Thisoccurrence serves to make the electron orbit unstable radially so thatelectrons are permitted to escape from it eithe in an inward or anoutward direction according to the sense in which the field of theauxiliary coil disturbs the balanced condition of the magnetic system.For the purpose of permitting orbit expansion, the direc- 3 tion ofenergization of the coils 5i and 52 should be such as to cause themagnetic field produced by these coils at and outside the normal orbitto oppose that produced by the coils 32 and 33. And to cause themagnetic flux enclosed by the orbit to be increased. This is broughtabout by causing the currents in coils 5i and 52 to flow in the samerotational direction as in coils 32 and 33.

On the other hand, in a case in which orbit contraction rather thanorbit expansion is desired (i. e. in a construction in which theintercepting target is inside the normal orbit) the magnetic fieldproduced at the normal orbit by the auxiliary coils should have the samedirection as that produced by the main coils, which can be brought aboutby currents of opposite rotation to those in the main coils. Moreover,in this case, the auxiliary coils should be inside the circumference ofthe smallest orbit the electrons are desired to attain upon energizationof the coils.

By appropriate arrangement of the coils 5| and 52, i. e. inside or nearthe orbital path of the accelerated particles, it is possible to causethe neutral point of the two coils, that is, the point of zero fieldattributable to the coils, to coincide with the orbital path. T is isadvantageous in that the radial gradient of the coil field is maximum atand near the aforesaid neutral point, this being the condition mostfavorable to disturbance of the stability of the electron orbit.

Inasmuch as the coils 5i and 52 are linked by a large proportion of theflux passing between the poles M and i5 and produced by the coils 32 and33, there is a voltage generated in the coils by this flux which mayhave an unfavorable reaction on the agency by which the coils 5i and 52are supplied with current. Moreover, the selfinductance of these coilstends to be quite high Fi l as a result of the fact that the fluxproduced by them has a substantially closed iron path through themagnetic cores 29 and 80. Both the feedback effect above referred to andthe self-inductance of the coils may be reduced by the use of additionalcompensating coil 54 and 55 connected in series with the coils 5| and 52and differentially wound with respect to the latter coils as indicateddiagrammatically in Fig. 4. Obviously with this arrangement any voltageinduced in the coils 5i and 52 by the variations of the magnetic flux issubstantially offset by an opposing voltage generated in coils 54 and55. Furthermore, assuming that the coils 5d and 55 have the same numberof turns as the coils 5| and 52, it is apparent that the former coilpair completely neutralizes the magnetizing effect of the latter pairinsofar as the magnetic flux through coils 5| and 52 is concerned. Thatis to say, in view of the mutually bucking efiect of the coils 5|, 52and 5B, 55, no flux attributable to these coils can exist inside thecoils 5i and 52. Since there is no other low reluctance path for fluxlinking the coils in question, the overall self-inductance of thecircuit in which the coils are included will be very much reduced andthe voltage required to energize the circuit will be lowered to areadily attainabl value.

A still further advantageous result gained by the use of coils 55 and 55arises from the fact that the presence of these coils tends to increasethe magnitude of the orbit-disturbing field within the space occupied bythe vessel I0.

In order to make the best use of the orbitexpanding coils, it isdesirable that their energization be appropriately correlated to theaction of the magnetic flux produced by the coils 32 and 33. This may bedone in one way by interconnecting the two field-producing systems by anarrangement such as that illustrated in Fig. 5. In this figure,represents the alternating current supply source by which the mainmagnetic flux is supplied. The coils 32 and 33, the coils 31 and 38 andthe coils 5!, 52, 54 and 55 correspond to the similarly numberedelements described in connection with Figs. 3 and 4.

The energizing system for the coils 5!, 52, etc. is coupled to the mainmagnetic flux by means of a coil which is disposed within the influenceof the said flux. This coil is in series through a phase shifting device65' with the primary winding of a peaking transformer 55 which connectswith the grid 61 of a discontinuously conductive discharge device 58 (e.g. a thyratron). The plate 69 of the device 68 is connected to oneterminal of a condenser 10 and is also connected to the positiveterminal ll of a unidirectional current supply source (not shown) bywhich the condenser i0 is charged during periods when the device isnon-conductive. A resistor 72 and a reactor 12', located as shown, serverespectively as a current limiting means and as a commutating agency forthe tube 58. The phase shifter 65' may be so adjusted that when the mainmagnetic flux approaches its peak value, the tube 68 is triggered by theaction of the peaking transformer 66 and the potential of the condenser1c is impressed across a resistor 73 which .is in circuit with thecathode id of the device. Since this resistor is in its turn connectedacross the coils 5!, 52, etc., these coils are abruptly energized andcause an immediate change in the distribution of the field between thepole pieces it and i5 (Fig. 1). Assuming that the coils 5| and 52 areexcited in the proper direction, this will lead at once to expansion ofthe orbit of gyration of the accelerated electrons and will permit themto impinge upon the exposed surface of the electrode 4| as previouslyexplained.

In order to assure the return of the device 08 (Fig. 5) tonon-conductive condition after a brief period of current flow, aninductance I may be connected in the discharge circuit of the device toproduce an instantaneous reversal of potential after the condenser I0 isdischarged.

The orbit-shifting system described in the foregoing has the primaryadvantage that it is highly positive and reliable in its action. Inaddition, it is characterized by the further advantage that it isreadily controllable both as to time of operation (e. g. by adjustmentof the elements of the circuit of Fi and as to the direction and forceof the electron diverting effects which it produces.

For some uses of the induction accelerator it is desirable that theaccelerated electrons be projected from the accelerating chamber in sucha way as to permit their effective utilization outside the chamber. Froma practical standpoint this means that the electrons must be projectedthrough a wall of the chamber in a reasonably well-defined beam. Thisobviously is a result which cannot be obtained merely by expanding theorbit of the electrons in the manner described in the foregoing for thereason that even if the expanded orbit is made to reach the wall of thecontaining vessel, any electrons which escape by penetration through thewall will be released in random directions.

A further important aspect of my invention consists in the provision ofmeans by which, after initial expansion of the electron orbit to acritical point, the electrons retained in the orbit may suddenly bewholly released from the influence of the guide field and allowed toescape in a preselected direction. The structural aspects of anarrangement which serves this end are shown in Figs. 6, 7 and 8 of thedrawings.

As in the construction previously described, electron acceleration isaccomplished within an annular glass vessel 80 by means of atime-varying field produced by coils 8| and 82 between appropriatelytapered pole pieces 83 and 84. .A low reluctance flux path is providedat the center of the pole system by a pair of laminated iron cylinders85 separated by insulating disks 85'. However, in this case theelectrode system by which the electrons to be accelerated are initiallyintroduced into the accelerating vessel is positioned near the innerperiphery of the vessel as indicated at 86. The energizing connectionsfor the injecting electrodes are brought across the bottom of the vessel80 from a stem press 88 by means of a cable 89 which is preferablyexternally coated with a conductive substance to prevent disturbance ofthe accelerating field by ac-- cumulation of electrostatic charges onthe cable. Once released into the accelerating chamber by the electrodestructure 86, the electrons are drawn into the accelerating orbit insubstantially the same manner as in the construction of Fig. 1.

In order to expand the orbit of the electrons after they have been fullyaccelerated, an auxiliary coil system comprising inner coils 92 and 93and outer coils 94 and 95 is provided. The respective coil pairs arediflerentially connected and are preferably in series for reasonspreviously given herein.

In addition to the orbit-expanding means Just described, there isfurther provided a magnetic structure -I00 which is 01 small dimensionsand which is enclosed within the accelerating vessel 00 mini; relativelynear its outer periphery. fins magnetic structure is or curved elongatedconfiguration (see Fig. 7) and includes a pair of opposed poles I02 and,I08 (Figs. 6 and 8). It is energized by means of an exciting winding I04having terminal connections I 05 which are brought through the wall ofthe enclosing vessel by means of a stem press I08.

' The disposition of the magnetic structure I00 is such that its fielddoes not affect the gyrating electrons as long as they are confined tothe normal accelerating orbit, i. e. the circular orbit indicated by thedash line A in Fig. 'I. The structure is, in fact, sufiiclentlydisplaced from this 1' it se that the electrons can be brought betweenits poles only after a relatively great expansion of the orbit has beenproduced. By this arrangement, it is possible to produce a result suchas that which is indicated diagrammatically in Fig. *7. In this figurethe dash lines B, C and D respectively indicate the successive turns ofthe stream of accelerated electrons as the orbit of the stream isprogressively increased by the expanding effect of the coils 92, 93,etc. (Fig. 6). It will be noted that the displacement between. turns Band C is relatively slight, but that this displacement increases as theorbit expansion continues to the point where the electrons are forcedinto the fringing field of the main magnetic system (i. e. where theconstraining effect of the field is considerably less). Accordingly, byappropriate disposition of the magnetic structure I00, that is, bydisposing it at a location where the distance between successive turnsof the expanding electron orbit is relatively great, it is possible toassure the result 40 that the outwardly spiralling electrons shall bebrought more or less suddenly into the region of influence of themagnetic structure I00. The field of this structure is of such strengthdirection as materially to augment the centrifugal tendency of theaffected electrons, thus permitting them to escape abruptly from theouter fringes of the main guide field.

The released electrons are free to follow a substantially straight linecourse and therefore impinge on the wallof the confining vessel afterleaving the magnetic structure I 00. In order to facilitate the use ofthe directed electron beam thus realized, it is expedient to provide inthe expected path of the beam a readily pervious window such as aspecially thinned portion in the container wall, such a window beingindicated at I08 in Fig. '2.

In order to obtain the results specified in the foregoing, it isdesirable that the energization of the magnetic structure I :18 becorrelated to the energization of the expanding coils 92, 98, etc., andin this connection it is appropriate that these elements be excited froma common source. This may be done, for example, by the use of a circuitarrangement such as that shown in Fig. 5 by placing the energizing coilI04 of the magnetic structure I00 in parallel with the coils of theorbit-expanding system.

Due to the fact that the magnetic structure I I00 is necessarily placedin relatively close proxfimity to the main accelerating orbit, there issome tendency for its field prematurely to disturb the symmetry of themain accelerating field prcduced between the poles 33 and Ii. In orderto minimize this effect, it is advantageous to provide in connectionwith the magnetic structure I shielding means which in a particular casemay comprise a sheet of conducting metal (e. g.

copper) bridging the gap between the poles of case with the field of themagnetic structure Hi0 when excited from an intermittently operatedsource of the character illustrated in Fig. 5.

The action of the magnetic structure I00 may well be described bycomparing it to a knife held at the outer edge of a spirally expandingbeam. If the beam is not spiralling outwardly rapidly but is movingoutwardly in very small steps, then the thickness of the knife edge willintercept a great deal of the beam. It is only when the distance betweensuccessive spirals is equal to or large compared with the width of theknife that a great deal of the beam can be efiectively shaved ofi. Inthe present connection, the width of the knife corresponds to the widthof the fringing fiux of the local magnetic field produced by thestructure Hill, and it is, therefore, desirable that the displacementbetween the successive electron gyrations C and D be at least as greatas this width.

While the invention has been described by reference to particularembodiments, it will be understood that numerous modifications may bemade by those skilled in the art Without actually departing from theinvention. I therefore aim in the appended claims to cover all suchequivalent variations as come within the true spirit and scope of theforegoing disclosure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A magnetic induction accelerator including an enclosure within whichcharged particles may execute orbital movements along a, generallycircular path, means in proximity to the said enclosure for producing atime-varying magnetic field linking the said path and producing anaccelerating electric force on charged particles within the enclosure,said means including juxtaposed pole pieces which are rotationallysymmetrical about an axis coincident with the axis of the said circularpath and which are shaped to produce a field distribution of such formas normally to confine particles within the enclosure to the saidcircular path while they are being accelerated, and means symmetricallydisposed with respect to the axis of said pole pieces for producing aradially symmetrical disturbance of the magnetic field between the polepieces of such magnitude as to permit deviation of the acceleratedparticles from the said orbital path.

2. A magnetic induction accelerator including an enclosure within whichcharged particles may execute orbital movements along a generallycircular path, means in proximity to the said enclosure for producing atime-varying magnetic field linking the said path and producing anaccelerating electric force on charged particles within the enclosure,said means including juxtaposed pole pieces which are rotationallysymmetrical about an axis coincident with the axis of the said circularpath and which are shaped to produce a field distribution of such formas normally to confine particles within the enclosure to the saidcircular path while they are being accelerated, and means operable topermit accelerated particles to deviate from said path, said last namedmeans comprising a pair of similar coils which are respectively disposedsymmetrically with respect to the axis of said pole pieces on oppositesides of the plane of the said orbital path, being of smaller diameterthan the path, and which are effective when energized to modify thedistribution of the magnetic field normally existing between the saidpole pieces.

3. A magnetic induction accelerator including an enclosure within whichcharged particles may execute orbital movements along a generallycircular path, means in proximity to the said enclosure for producing atime-varying magnetic field linking the said path and producing anaccelerating electric force on charged particles within the enclosure,said means including juxtaposed pole pieces which are rotationallysymmetrical about an axis coincident with the axis of the said circularpath and which are shaped to produce a field distribution of such formas normally to confine particles within the enclosure to the saidcircular path while they are being accelerated, a first pair of similarcoils respectively positioned on opposite sides of the plane of the saidorbital path and coaxial with it, said coils being of smaller diameterthan the said orbital path, and a second pair of coils differentiallyenergized withrespect to the first pair and of larger diameter than thesaid orbital path, the individual coils of said second pair being alsodisposed on opposite sides of the plane of the orbital path wherebyconjoint energization of both pairs of coils produces sufficientmodification of the magnetic field between the said pole pieces topermit deviation of the accelerated particles from the said orbitalpath.

4. A magnetic induction accelerator including a chamber within whichorbital gyrations of charged particles may occur, means in proximity tothe chamber for producing a time-varying magnetic field of such spacedistribution as normally to confine charged particles within the chamberto a restricted orbital path while continuously accelerating them bymeans of the associated induced electric field along such path, meanswhich is symmetrically arranged with respect to said path and isoperable to modify the distribution of the said magnetic field to permitaccelerated particles to deviate from said orbital path while stillremaining within the infiuence of said acceleratingelectric field, andfurther means operative upon the accelerated particles only after theyhave experienced a predetermiend critical deviation from said orbitalpath for abruptly removing the affected particles from the influence ofthe accelerating field.

5. A magnetic induction accelerator including a, chamber within whichorbital gyrations of charged particles may occur, means in proximity tothe chamber for producing a time-varying magnetic field of such spacedistribution as normally to confine charged particles within the chamberto a restricted orbital path while continuously accelerating them bymeans of the associated electric field along such path, means which issymmetrically arranged with respect to said path and is operable tomodify the distribution of the said magnetic field to permit acceleratedparticles to deviate from said orbital path while still remaining withinthe influence of said accelerating electric field, and further means forproducing a localized magnetic field which is operative upon theaccelerated particles only after they have experienced a predeterminedcritical deviation from said orbital path, said last named means beingeffective abruptly to remove particles afiectecl by it from theinfluence of the accelerating field so as to facilitate theirutilization outside the accelerating chamber.

6. A magnetic induction accelerator including a chamber within whichorbital gyrations of charged particles may occur, means in proximity tothe chamber for producing a time-varying magnetic field of such spacedistribution as normally to confine charged particles within the chamberto a restricted orbital path while continuously accelerating them bymeans of the associated electric field along such path, means dis= posedcoaxially with respect to said orbital path and being operable to modifythe distribution of the said magnetic field to displace the orbital pathof said particles while still remaining within the influence of saidaccelerating electric field, a magnetic structure 'within theaccelerating chamber and energizing means for said structure correlatedwith said field-distribution modifying means for producing a localizedmagnetic field which is traversed by the accelerated particles onlyafter they have experienced a predetermined critical deviation from saidorbital path. said magnetic structure being efiective to assure at leastthe partial collimation of particles influenced by it.

7. A magnetic induction accelerator including a chamber within whichorbital gyrations of charged particles may occur, means in proximity tothe chamber for producing a time-varying magnetic field of such spacedistribution as normally to confine charged particles within the chamberto a restricted orbital path while continuously accelerating them bymeans of the associated electric field along such path, mean operablctomodify the distribution of the said magnetic field to permit acceleratedparticles to deviate from said orbital path while still remaining withinthe influence of said accelerating electric field, a magnetic structurefor producing a localized magnetic field which is traversed by theaccelerated particles only after they have experienced a predeterminedcritical deviation from said orbital path, said magnetic structure beingefiective to remove particles afiected by it from the influence of theaccelerating electric field, and shielding means for preventing thefield of the magnetic structure from extending into the said orbitalpath.

8. A magnetic induction accelerator including a chamber within whichorbital charged particles may occur, means in proximity to the chamberfor producing a time=varying magnetic field of such space distributionas normally to coufine charged particles within the chamber to arestricted orbital path while continuously accelerating them by means ofthe as sociated electric field along such path, means op-= yrations ofera'ole to modify the distribution of the said magnetic field to permitaccelerated particles to deviate from said orbital path while stillremaining within the influence of Said accelerating electric field, amagnetic structure for producing a localized magnetic field which istraversed by the accelerated particles only after they have experienceda predetermined critical deviation from said orbital path, said magneticstructure being effective to remove particles aifected by it from theinfluence of the accelerating field, and a conductive metal shieldassociated with said magnetic structure for preventing the field of thestructure from extending into the said orbital path.

9. A magnetic induction accelerator including the combination of anannular evacuated enclosure, means for injecting electrons into saidenclosure, means in proximity to said enclosure for producing atime-varying magnetic field whereby an electric force is exerted causingelectrons to execute accelerated orbital movements in the circular pathprovided by said enclosure, said means including juxtaposed pole piecewhich are rotationally symmetrical about an axis coincident with theaxis of the said circular path and which are shaped to producea fielddistribution of such form as normally to confine electrons within theenclosure to said circular path while they are being accelerated, andauxiliary fieldproducing windings arranged above and below said circularpath and being symmetrically disposed with respect to the axis of saidpole pieces for modifying the magnetic field between the pole piecesthereby causing predetermined deviation to occur of the acceleratedelectrons and target means upon which said electrons may be caused toimpinge.

10. A magnetic induction accelerator including the combination of anannular evacuated enclosure, means for injecting electrons into saidenclosure, means in proximity to said enclosure for producing, atime-varying magnetic field whereby an electric force is exerted causingelectrons to execute accelerated orbital movements in an annular pathprovided by said enclosure, said means including juxtaposed pole pieceswhich are rotationally symmetrical about an axis coincident with theaxis of the said annular path and which are shaped to produce a fielddistribution of such form as normally to guide electrons within theenclosure to an annular path while they are being accelerated, andauxiliary fieldproducing means which is rotationally symmetrical withrespect to said path and is operabie to modifythe distribution of saidmagnetic field to cause controlled deviations to occur of theaccelerated electrons from their original annular path.

mrmm 'v'v'. WEST.

